ANTIGENS, HAPTENS, ANTIBODIES, ETC. 429 



antiserum and of kcphaliii to rabbit antisemm, but not 



vice versa. 



Globulins are usually considered to have approximately 

 spherical molecules but as a result of comparison of their 

 behaviour in the ultracentrifuge, and studies of viscosity 

 and electrophoresis it is becoming obvious that they 

 must be elliptical or even rod shaped. Serum globulin in 

 surface films opens up into fibre like molecules very 

 readily — a state which is associated with denaturation. 

 The normal ratio of length to breadth seems to lie 

 between 7 to 1 and 10 to 1, although for horse anti- 

 pneumococcus globulin the ratio is reported as 20 to 1. 



The molecules have a short axis 37 A long whilst the long 



axis varies between 270 and 350 A long. 



Antibodies are comj)aratively labile substances ; they 

 are much weakened by heating at 60° to 70° C, and are 

 rapidly destroyed on boiling. They are more stable to 

 dry heat (as are most proteins) and are not affected by 

 cold. Prolonged heating at 57° C. precipitates antitoxins 

 along with the globulins. The effect of heat mns parallel 

 with denaturation and is independent of the particular 

 serum in which the antibody is present. Antibodies are 

 most resistant to heat at neutrality, the rate of destruction 

 being increased by acid or alkali. If denaturation of the 

 protein is hindered by the addition of sodium chloride 

 (above 2N), glycerol or sucrose or by dilution of the 

 serum, the destruction of the antibody is retarded. The 

 resistance of antibodies to heat ajijparently varies from 

 antibody to antibody ; thus the flagellar antibody of 

 the hog cholera bacillus will withstand 90° C. for twenty 

 minutes, whilst the somatic antibody is destroyed at 

 75° C, and loses half its activity at 65° C. in the same 

 time. The differences are due, however, not to differences 

 in heat stability but to the fact that the apparently more 

 susceptible antibodies form complexes with non-specific 

 nitrogen compounds, such as albumin, in the serum 



